Iron

ABSTRACT

An iron including heating means and a sole plate wherein means for controlling the heating means is provided in the sole plate.

Umted States Patent 11 1 1111 3,732,394 Cusworth 1 May 8, 1973 1 IRON[58] Field of Search ..219/243, 245, 248, [75] Inventor: MauriceCusworth, Gal-forth, near 100/93 Leeds, England /2224, 28

. 56 R 1 Ct d [73] Ass1gnee: Isaac Bralthwalte & Son Engmeers 1 1 eerences Ltd., Kendal, Westmorland, UNITED STATES PATENTS England3,286,077 11/1966 Radford etal ..219 251 [22] Filed: Feb. 17, 19712,694,766 11/1954 Ireland ..219/254 X [21] Appl' 115379 PrimaryExaminerC. L. Albritton Attorney-James E. Nilles [30] ForeignApplication Priority Data Feb. 19, 1970 Great Britain ..7,905/70 [57]ABSTRACT An iron including heating means and a sole plate [52] U.S.Cl...219/25l, 38/82, 219/254 wherein means for controlling the heatingmeans is [51] Int. Cl. .;.....D06f 75/26 provided in the sole plate.

6 Claims, 2 Drawing Figures ama,

IRON

This invention relates to an iron and more particularly to an iron, thetemperature of which is controllable.

According to the invention there is provided an iron including heatingmeans and sole plate wherein means for controlling the heating means isprovided in the sole plate.

Preferably, the means for controlling the heating means comprises athermistor and the heating means comprises one or more electricalheating elements located in the sole plate.

The iron may be of the all electric type or what is termed a steamelectric iron in which steam is sprayed from perforations in the soleplate.

The circuitry by which the thermistor controls the element may be of anysuitable design. It is preferred that the circuitry be designed tomaintain the iron at any desired temperature preferably from 90 to 260C.

A specific embodiment of the invention will now be described by way ofexample with reference to the accompanying drawings in which:

FIG. 1 is a section through an iron; and

FIG. 2 is a circuit diagram of a preferred control circuit.

Referring to FIG. 1, the iron comprises a sole plate 1 which ispreferably made of bronze with a chrome finish, and which is secured toan element plate 2, made for example of aluminum, by studs of which one9 is shown. A bore 7 is formed through the element plate and a bore 8 isformed in the sole plate such that when the element and sole plates aresecured together the bores are co-axial. The bore 8 extends from theface of the sole plate adjacent the element plate to a point close tothe face of the sole plate remote from the element plate, but as shownin FIG. 1 does not extend completely through the sole plate.

A thermistor holder 10 is provided in the bores 7 and 8 and a thermistor11 is located in the holder. The thermistor is coupled into a controlcircuit as shown in FIG. 2 via a terminal 6, the control circuit in thepresent embodiment being located externally of the iron. The thermistoris an inert or solid state device.

A moulded handle and cover-3, which may for example be made of plasticsmaterial is secured to the element plate by studs, one of which 12 isshown. An asbestos sheet 13 is interposed between the cover and theelement plate.

The invention is not restricted to the abovedescribed embodiment manyvariations, such as would readily occur to one skilled in the artfalling within the scope thereof. Thus the control circuit may beprovided within the casing instead of externally thereof.

A suitable control circuit for the iron just described is shown in FIG.2. The temperature of an iron 15 is controlled by means of a thermistor16 the thermistor itself being controllable by means of a variableresistance 17 When the heating element is connected to the currentsupply by means of switch 18 the iron .will heat up and as it does sothe resistance of the thermistor will decrease. This has the effect ofreducing the current drawn by the iron heater elements so that the heatof the iron can be limited to a value determined by the variableresistor. As the iron starts to cool down the resistance of thethermistor will rise so that the heater elements again draw sufficientcurrent to V heat the iron. It will be appreciated that with thisarrangement very close control of iron temperature can be maintained. AsFIG. 2 shows, power for iron 15 is applied at terminals 20 and 22, andafter passing through a short-circuit protection fuse 24, a MAINS ONindication is provided by a neon lamp 26. Surge and radio interferenceprotection is provided by a series choke 28 and a shunt capacitor 30 atthis point in the circuit.

A portion of the alternating current across terminals 20 and 22 isrectified by a bridge rectifier 32 and produces across a zener diode 34a series of flat-topped waves recurring every half cycle of the ACfrequency. Across the points 36 and 38 is connected the seriescombination of a ohm resistor 40, SET TEMP. variable resistor 17, andthermistor 16, the latter being embedded in brass probe 10 in the ironsole plate 1. This combination behaves as two arms of a Wheatstonebridge, thepotential at the connecting point of a 1K ohm resistor 42 inseries with the base 44b of a 2N 3391 transistor 44 being inverselyproportion to the thermistor (and hence the iron sole plate)temperature. The effect of transistor 44 is to quickly charge a 0.47 uFcapacitor 46 in the emitter circuit to the potential on the baseterminal of transistor 44. During the remainder of the flat-topped waveperiod, capacitor 46 is further charged from bridge rectifier 32 througha 1M ohm variable resistor 48. Thus the potential at a point 50 duringone of the periods is a quick step to a level inversely proportional toiron sole plate temperature followed by a gradual linear rise dependentonly upon the setting of the 1M ohm variable resistor48. This potentialis applied to the emitter 52e of a 2N 2646 unijunction transistor. Thefiring potential of transistor 52 is determined purely by the voltage atpoints 36 and 38 and the ratio of series resistors 54 and 56 in bothbase leads and is, therefore, constant. These two base resistors(comprising 1K ohm 54 from point 36 and the P.T. primary winding 56 frompoint 38), together with the inherent internal resistance of the baseleads, constitute the two other arms of the Wheatstone bridge referredto earlier.

Whenever the potential of point 50 exceeds the firing potential ofunijunction transistor 52 the stored energy of 0.47 uF capacitor 46 isimmediately delivered to the primary winding 36 of the pulse transformerP.T. and thence via the secondary winding 58 into the gate terminal 60gof a triac 60. This causes triac 60 to turn on, connecting the load (theiron 15) to terminals 20 and 22 for the remainder of the half cycle.Following this power pulse into iron 15 the firing procedure must bere-initiated.

Thus, with iron 15 cool the thermistor l6 resistance will be high andthe potential at point 50 will be high at an early point in the halfcycle and rises higher thereafter. The initial potential at point 50will be sufficient to cause unijunction transistor 52 to tire and thustriac 60 will deliver almost a full half cycle pulse to the element ofiron 15 during each half cycle. When iron 15 achieves the desiredtemperature, the thermistor 16 resistance will be lower and the initialquick rise of potential at point 50 will be insufficient to fireunijunction transistor 52, this then occurring later in the half cycleduring the linear ramp, the amount of delay depending on the precisetemperature of the thermistor and the slope setting, determined by l uohm variable resistor 48. The power pulses to the element of iron arethus shortened and stability is reached when the average power has beenreduced until it is just sufiicient to maintain sole plate 1 at thedesired temperature. As more power is required when iron 15 is put towork, the temperature must drop slightly in order to allow the ramp atpoint 50 to increase its initial potential and thus fire unijunctiontransistor 52 earlier in each half cycle. Conversely, a rise intemperature causes the ramp to start from a lower point and thus fireunijunction transistor 52 later. The limits of operation between full-onand full-off are determined by the slope of the ramp (and hence by thesetting of 1M ohm variable resistor 48) and the control for this slopeis, therefore, termed the Proportional Band.

The triac 60 is further protected from transient voltage surges acrossterminals and 22 by a diverting network comprising a 1K ohm resistor 62and a 0.047 uF capacitor 64. Thus, any surges by-pass triac 60 and aredissipated harmlessly in the 64 element of iron 15.

1 claim:

1. In combination: an iron having electrical heating means energizablefrom an electric current source and adapted to heat a sole plate, and acontrol circuit for said iron comprising,

a temperature sensitive element responsive to the temperature of saidsole plate to exhibit a change in an electrical value thereof,

a capacitor,

means responsive to a change in the electrical value of said element toeffect charging of said capacitor,

first switching means actuatable in response to discharge of saidcapacitor,

and second switching means actuatable in response to actuation of saidfirst switching means to .connect saidheating means for energizationfrom said source.

2. A control circuit according to claim 1 including adjustable variableresistance means to regulate the rate of charge of said capacitor. J

3. A control circuit according to claim 1 wherein said capacitor isrepeatedly charged and discharged in response to a charge in theresistance of said element and wherein said second switching means isactuatable repeatedly in response thereto to provide repeated connectionof said heating means to said source whereby power pulses are suppliedto said heating means from said source.

4. A control circuit according to claim 3 wherein said means responsiveto a charge in the resistance of said element to effect charging of saidcapacitor comprises a transistor; wherein said first switching meanscomprises a unijunction transistor; and wherein said second switchingmeans comprises a 'triac type solid state device.

5. A control circuit according to claim 4 wherein said unijunctiontransistor is coupled to said triac type device by pulse transformermeans.

6. A control circuit according to claim 5 including rectifying meansenergizable from said electric current source, and wherein saidtemperature sensitive resistance element, said capacitor, saidtransistor and said uni unction transistor are in circuit with saidrectifying means.

1. In combination: an iron having electrical heating means energizablefrom an electric current source and adapted to heat a sole plate, and acontrol circuit for said iron comprising, a temperature sensitiveelement responsive to the temperature of said sole plate to exhibit achange in an electrical value thereof, a capacitor, means responsive toa change in the electrical value of said element to effect charging ofsaid capacitor, first switching means actuatable in response todischarge of said capacitor, and second switching means actuatable inresponse to actuation of said first switching means to connect saidheating means for energization from said source.
 2. A control circuitaccording to claim 1 including adjustable variable resistance means toregulate the rate of charge of said capacitor.
 3. A control circuitaccording to claim 1 wherein said capacitor is repeatedly charged anddischarged in response to a charge in the resistance of said element andwherein said second switching means is actuatable repeatedly in responsethereto to provide repeated connection of said heating means to saidsource whereby power pulses are supplied to said heating means from saidsource.
 4. A control circuit according to claim 3 wherein said meansresponsive to a charge in the resistance of said element to effectcharging of said capacitor comprises a transistor; wherein said firstswitching means comprises a unijunction transistor; and wherein saidsecond switching means comprises a triac type solid state device.
 5. Acontrol circuit according to claim 4 wherein said unijunction transistoris coupled to said triac type device by pulse transformer means.
 6. Acontrol circuit according to claim 5 including rectifying meansenergizable from said electric current source, and wherein saidtemperature sensitive resistance element, said capacitor, saidtransistor and said unijunction transistor are in circuit with saidrectifying means.